1. Field of the Invention
The present invention relates to a rolling bearing.
2. Description of the Related Art
Rolling bearings configured to support rotation shafts of various types of machinery are required to have such a reliability that seizure does not occur. Therefore, grease lubrication that provides high lubricating performance is widely employed (see, for example, Japanese Patent Application Publication No. 2016-23647 (JP 2016-23647 A)).
The use of grease lubrication is proposed for rolling bearings to be used under an environment that involves high-speed rotation.
FIG. 5 is a sectional view illustrating an example of a related-art rolling bearing. In the case of grease lubrication, seals 97 and 98 serving as sealing devices are provided on both axial sides of an annular space 94 formed between an inner ring 91 and an outer ring 92. In order to achieve high-speed rotation, the seals 97 and 98 are labyrinth seals (non-contact seals). That is, labyrinth clearances 97a and 98a are formed between the inner ring 91 and the seals 97 and 98, thereby preventing leakage of grease.
A cage 96 illustrated in FIG. 5 is a so-called machined cage having a first annular portion 96a, a second annular portion 96b, and a plurality of cage bars 96c. The first annular portion 96a is located on one axial side of balls 93. The second annular portion 96b is located on the other axial side of the balls 93. The cage bars 96c couple the annular portions 96a and 96b to each other. The machined cage 96 is excellent in rotational stability, and is often used for rolling bearings in applications to high-speed rotation.
The rolling bearing illustrated in FIG. 5 is an angular contact ball bearing 90. The balls 93 are in contact with the inner ring 91 and the outer ring 92 at predetermined angles (contact angles). In the case of the angular contact ball bearing 90, a shoulder diameter D2 of the inner ring 91 on the other axial side (right side in FIG. 5) is larger than a shoulder diameter D1 of the inner ring 91 on one axial side (left side in FIG. 5) (D1<D2). Therefore, when the angular contact ball bearing 90 (inner ring 91) rotates, a centrifugal force causes an action that forces the grease in the annular space 94 from one axial side to the other axial side (from the left side to the right side in FIG. 5). This action intensifies particularly when the bearing rotates at a high speed. Thus, the grease in the annular space 94 concentrates in a space 95 on the other axial side, thereby causing imbalance in the grease.
When the grease concentrates in the space 95 on the other axial side, the grease is agitated by the second annular portion 96b of the rotating cage 96. Due to influence of the agitation, the grease is likely to pass through the labyrinth clearance 98a, thereby causing a problem of leakage of the grease. The leakage of the grease leads to insufficient lubrication, which may cause troubles such as seizure, temperature rise, and wear. The grease that concentrates in the space 95 is agitated and sheared by the second annular portion 96b, and the life of the grease may be shortened.
The action that forces the grease from one axial side to the other axial side due to the rotation of the bearing may also be caused by factors other than the structure in which the shoulder diameters D1 and D2 of the inner ring 91 are different from each other. Although illustration is omitted, the action that forces the grease from one axial side to the other axial side may be caused, for example, when a shoulder diameter of the outer ring on the other axial side is larger than a shoulder diameter of the outer ring on one axial side, or when rolling elements (balls) spin along with the rotation of the bearing. Even if the sealing device is not the labyrinth seal but a contact seal, the problem of leakage of the grease to the outside of the bearing occurs.